Selective destruction of certain neurons marks many of the neurological diseases, including the cerebellar degenerations and motor neuron diseases such as ALS. Considerable evidence suggests that the degeneration in these diseases may result from excitotoxicity, in which excessive activation of glutamate receptors leads to neuronal damage. Furthermore, the best models suggest that the damage to the two neuronal types destroyed in these diseases, cerebellar Purkinje cells and spinal motor neurons, is mediated by the AMPA subtype of glutamate receptors. This project will study the mechanism of the selective vulnerability of these neurons by relating their particular patterns of AMPA receptor expression at the molecular level to functional receptor properties relevant to toxicity. In particular, expression of AMPA receptors that are relatively resistant to desensitization, or of receptors that have higher permeability to Ca2+ may render these cells selectively vulnerable to glutamate toxicity. These issues will be investigated in the following specific aims: 1 To assess whether the functional properties of AMPA receptors in Purkinje neurons are determined by the AMPA subunit mRNA expression pattern using single cell PCR amplification in conjunction with patch-clamp electrophysiological studies. 2. To explore the relationship of the desensitization and Ca2+ permeability of AMPA receptors expressed in Purkinje cells to their selective vulnerability in electrophysiological studies correlated with specific toxicity in culture. 3. To define the functional properties of AMPA receptors and their molecular expression pattern of motor neurons. Again, the determination of desensitization and Ca2+ permeability by subunit expression will be studied using single cell PCR and patch-clamp studies. 4. To examine the receptor subtypes responsible for selective vulnerability in spinal motor neurons in organotypic spinal cord slice cultures, identifying the properties of AMPA receptors responsible for selective vulnerability. Understanding how the properties of AMPA receptors can lead to selective damage to Purkinje cells and spinal motor neurons may hold the key to understanding the mechanisms of their degeneration and to recognition of the best molecular targets for neuroprotection in cerebellar degenerations and ALS.